I tried to make a sentence saying that since I don't have the key I cannot go inside the room that has a kettle:
鍵がないからヤカンがある部屋に入れなかった
But I was told that it sounds better if I changed it for
鍵がないからヤカンのある部屋に入れなかった
What's the grammatical reason that explains this?
The grammar behind this is explained in this question, although you may already know this: How does the の work in 「日本人の知らない日本語」?
I personally think this sentence is perfectly fine and natural regardless of whether you use が or の. Someone might feel the sentence sounds slightly more "soft" or "sophisticated" with の, but this is very subjective. I think you can safely ignore the difference unless you're interested in aesthetic writing.
